The cherished dog who sleeps on your couch or snores under your arm while you're eating supper has a far wilder past. Dogs developed from gray wolves under the direction of domestication at some time to become the varied fuzzbutts that now bring us so much joy in our homes and hearts.
However, the precise timing and manner of this procedure remain a mystery. Ancient DNA is now offering some insight on how wolves evolved into some of our finest non-human pals, including wolf DNA that has been kept in permafrost for tens of thousands of years.
"Through this project we have greatly increased the number of sequenced ancient wolf genomes, allowing us to create a detailed picture of wolf ancestry over time, including around the time of dog origins," said Anders Bergström, a geneticist from The Francis Crick Institute in the UK.
"By trying to place the dog piece into this picture, we found that dogs derive ancestry from at least two separate wolf populations – an eastern source that contributed to all dogs and a separate more westerly source that contributed to some dogs."
Canis familiaris is the species to which all domestic dogs today, from the tiniest chihuahua to the largest mastiff, belong. And they all share wolf lineage with the gray wolf of today (Canis lupus). However, the timing is unclear and contentious. According to dubious claims made by certain experts, the process started more than 100,000 years ago.
In recent research by Bergström and his associates, 32 canines with ages ranging from 100 to 32,000 years ago were studied using their DNA. They discovered that dog species had diverged by 11,000 years ago, proving that it must have occurred earlier. Most scientists agree that domestication, and subsequently diversity, started between 40,000 and 20,000 years ago, maybe more than once, in various regions of the planet.
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| 'Dogor', an 18,000 year-old wolf puppy from Yakutia. (Sergey Fedorov) |
The new research is based on 72 ancient wolf genomes, 66 of which were recently scanned for this study. These genomes span over 30,000 generations of wolves in Europe, Siberia, and North America and date back 100,000 years.
These were contrasted with 68 genomes from other canid species, including coyotes, ancient and modern dogs, and modern wolves.
Among the samples were several well-known recent discoveries, such as the 32,000-year-old skull of a wolf, also from the Siberian permafrost, and the almost well preserved cub Dogor, trapped for 18,000 years in the Siberian permafrost.
A brown fuzzy wolf-like animal placed on a table
According to the genomes, both ancient and contemporary dogs are more closely connected to prehistoric wolves that lived in Asia than those that did in Europe. This shows that, rather than the West, the East may have been where domestication and diversity first started.
But something didn't seem right. The DNA of early dogs in Northeastern Europe, Siberia, and the Americas comes entirely from a wolf population in the east. Early wolves with ties to contemporary populations in Southeast Eurasia contributed DNA to dogs from the Middle East, Africa, and the southern part of Europe.
This may confirm earlier discoveries that dogs were domesticated more than once and in many locations throughout the world. It could also imply that wolves from the wild were first tamed in the East before being combined with dogs.
Since none of the genomes in the research are exact matches, it is unclear which of these situations may have actually occurred. More information is required.
The investigation helped the group understand more about prehistoric wolves and their development. They focused on a gene variation that, over the course of around 10,000 years, changed from being extremely rare to practically universal. IFT88, a gene that plays a role in the growth of the head and jaw bones, is affected by this mutation and is still seen in practically all dogs and wolves today.
Although the research is unsure of the exact cause of this mutation's widespread occurrence, it may be related to natural selection. Perhaps the sorts of accessible prey made the modifications brought about by the mutation particularly advantageous. It's also possible that the gene has undiscovered functions and that the mutation has some unintended advantages.
"This is the first time scientists have directly tracked natural selection in a large animal over a time-scale of 100,000 years, seeing evolution play out in real time rather than trying to reconstruct it from DNA today," remarked Pontus Skoglund, a geneticist and senior author who works for Crick.
"We found several cases where mutations spread to the whole wolf species, which was possible because the species was highly connected over large distances. This connectivity is perhaps a reason why wolves managed to survive the ice age while many other large carnivores vanished."
According to these results, such temporally extensive whole-genome research can provide us with considerably more in-depth understandings of how species migrate and change through time.
The team will now attempt to focus on specifically identifying which wolves were the forerunners of contemporary dogs. In order to cover all of the planet, the team is widening their research.
The research has been published in Nature.
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